Every link provided on this page are referral links, but are services I genuinely use and is trustable enough for me to share them to you. Don't take my word alone, though, and always check them yourselves despite all my efforts to give you a fair description of these websites.
"All your favourites games for Steam, Origin, Battle.net, Uplay and Indie games up to 70% off! Digital games, Instant delivery 24/7!"
Click here for more details! (I get 3% of the game you've bought by clicking on the link and 1% of each game bought by a referred account).
Tips: Although it never happened to me, the service can send you an invalid key since this is a gray market, so pay with Paypal in order to claim a refund if such a thing happen to you.